Variable Population Demographics of a Coral Reef Fish Across Vertical Spatial Scales

With the degradation of shallow coral reefs, deeper reefs that are buffered from anthropogenic impacts, storms, and temperature fluctuations may be important refuges for coral reef organisms. Mesophotic coral ecosystems, found at depths of between 30 and 150 m, share many of the same fish taxa that are found on shallower reefs, however, depth driven differences in coral reef habitats likely influence fish population demographics, and may have consequences for population persistence and connectivity. We compared size, growth, and reproductive output of the bicolor damselfish (Stegastes partitus) across shallow (upper shelf <10 m) and mid-depth reefs (lower shelf 20-30 m) in the Florida Keys, and mesophotic reefs (60-70 m) on the west Florida Shelf. Otolith-derived ages indicated that bicolor damselfish found on mesophotic reefs reached larger asymptotic sizes and had longer lifespans than fish found in shallower habitats. Based on fecundity estimates using oocyte counts, mesophotic reef fish also had higher reproductive output. Results of this study indicate that by supporting populations of large, long-lived individuals, mesophotic reef environments may be important sources of larvae for reef fish populations and valuable refuges for coral reef fish.